Melanins are pigments of high molecular weight formed by oxidative polymerization of phenolic or indolic compounds. In this present study, a black pigment was isolated from the fermentation broth of Ophiocordyceps sinensis, an entomogenous fungus which is endemic to the Tibetan Plateau by alkaline extraction, acid hydrolysis, and repeated precipitation. It was designed as melanin since the physical and chemical properties including its ultraviolet (UV) and infrared (IR) spectra of the black pigment conformed to the characteristic of melanin and similar to the commercial synthetic melanin. The antioxidant activity of melanin derived from O. sinensis was evaluated. They showed much stronger scavenging abilities on 1,1-diphenyl-2-picrylhydrazyl (DPPH center dot) and the chelating ability on ferrous ions than that of the water extract from the mycelia of O. sinensis, with IC50 value 18.51 +/- 0.85 mu g/ml and 2.58 +/- 0.26 mu g/ml, separately. This is the first report of melanin from O. sinensis and will be helpful for the study on the physiology and the artificial cultivation of this fungus, an endangered species. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.